- Deliverable Use The Atc Hazards By Location Webpage To Obtain The Seismic Acceleration Parameters S And Ss For The P 1 (75.85 KiB) Viewed 52 times
11.4.3 Site Class. Based on the site soil properties, the site shall be classified as Site Class A, B, C, D, E, or F in accordance with Chapter 20. Where the soil properties are not known in sufficient detail to determine the site class, Site Class D, subject to the requirements of Section 11.4.4, shall be used unless the authority having jurisdiction or geotechnical data determine that Site Class E or F soils are present at the site. For situations in which site investigations, performed in accor- dance with Chapter 20, reveal rock conditions consistent with Site Class B, but site-specific velocity measurements are not made, the site coefficients Fa, Fy, and FPGA shall be taken as unity (1.0). 11.4.4 Site Coefficients and Risk-Targeted Maximum Considered Earthquake (MCE) Spectral Response Acceleration Parameters. The MCER spectral response acceleration parameters for short periods (SMS) and at 1 s (SMI), adjusted for site class effects, shall be determined by Eqs. (11.4-1) and (11.4-2), respectively. SMS=FgSs SM1=F₁S₁ where Ss = the mapped MCER spectral response acceleration parameter at short periods as determined in accordance with Section 11.4.2, and S₁ = the mapped MCER spectral response acceleration parameter at a period of 1 s as determined in accordance with Section 11.4.2 where site coefficients F and F, are defined in Tables 11.4-1 and 11.4-2, respectively. Where Site Class D is selected as the default site class per Section 11.4.3, the value of F shall not be less than 1.2. Where the simplified design procedure of Section 12.14 is used, the value of F₁ shall be determined in accordance with Section 12.14.8.1, and the values for F, SMS, and SM need not be determined. Site Class E F Table 11.4-1 Short-Period Site Coefficient, F, Mapped Risk-Targeted Maximum Considered Earthquake (MCE) Spectral Response Acceleration Parameter at Short Period Ss ≤0.25 0.8 0.9 1.2 1.0 See See Section Section 11.4.8 See See See See Section Section Section Section Section Section 11.4.8 See See 11.4.8 11.4.8 11.4.8 11.4.8 11.4.8 11.4.8 Note: Use straight-line interpolation for intermediate values of S,. (11.4-1) (11.4-2) 0.8 0.9 1.3 1.6 2.4 Sg-0.5 S₂-0.75 Sg-1.0 Sg-1.25 Sg 21.5 0.8 0.9 1.3 1.4 1.7 0.8 0.9 1.2 1.2 1.3 0.8 0.9 1.2 1.1 0.8 0.9 1.2 1.0 See Section 11.4.8 D E F Spectral Response Acceleration, Sa (g) Sos 0.8 0.8 Sp 0.8 0.8 1.5 1.5 2.4 4.2 0.8 0.8 0.8 0.8 0.8 0.8 1.4 2.2 1.7⁰ See See Section Section 11.4.8 See 11.4.8 11.4.8 11.4.8 See See See Section Section Section Section 11.4.8 11.4.8 11.4.8 11.4.8 11.4.8 11.4.8 See See Section Section Note: Use straight-line interpolation for intermediate values of S₁. "Also, see requirements for site-specific ground motions in Section 11.4.8. 1.5 1.5 2.0° 1.9⁰ See See Section Section 0.8 0.8 1.5 1.8" See Section 11.4.8 -S.-Sp 1.0 Period. 7 (sec) FIGURE 11.4-1 Design Response Spectrum 11.4.5 Design Spectral Acceleration Parameters. Design earthquake spectral response acceleration parameters at short periods, Sps, and at 1-s periods, Sp, shall be determined from Eqs. (11.4-3) and (11.4-4), respectively. Where the alternate simplified design procedure of Section 12.14 is used, the value of Sps shall be determined in accordance with Section 12.14.8.1, and the value for Sp₁ need not be determined. Sps= SMS (11.4-3) SDI = (11.4-4) 11.4.6 Design Response Spectrum. Where a design response spectrum is required by this standard and site-specific ground motion procedures are not used, the design response spectrum curve shall be developed as indicated in Fig. 11.4-1 and as follows: Sa S₁ = Sps (0.4+0.67) 1. For periods less than To, the design spectral response acceleration, S₁, shall be taken as given in Eq. (11.4-5): (11.4-5)